1. Field of the Invention
The invention relates to tape recording and reproducing apparatus and particularly to such apparatus which customarily uses very small, micro cassettes in applications where relatively low frequency recordings and very slow moving tape require a relatively large playback/reproducing head for increased signal to noise (S/N) ratio.
2. Description of the Prior Art
Prior art magnetic tape recorder-players have progressed from relatively large reel-to-reel tapes, to 8-track cartridges and conventional cassettes, to the most recent micro or miniature tape cassettes. Prior to the introduction of the micro cassette, the relatively large size of tape reels necessitated that the tape recording or playing head be relatively distant from all electric motors conventionally used in tape decks; i.e. reel drive motors, pinch roller and capstan drive motor, and other electric motors or solenoids typically used in recorder-players. In such systems, there was limited concern for electrical or magnetic flux field interference with the head reading/recording functions due to the inherent relatively large separation of the head from all electric motors disposed within or around the recorder-player system.
However, with the advent of micro and miniature cassettes, and in particular in consideration of specialized very slow moving tape applications for relatively long record and play periods, combined with very high amplification required for the slow moving tape to adequately replay the recording, and the need to record relatively low frequency signals, existing tape deck systems do encounter increased noise and decreased signal to noise (S/N) ratio due to decreased signal sensitivity and due to proximity of various electric motors, i.e. reel motors, capstan motor and other operating motors, inductors or solenoids, all contributing in a significant manner to electric or magnetic flux interference with the head reading from or writing to a magnetic tape.
Generally speaking, in the reproducing, the magnetization of the tape produces flux in the core of the playback head, and as this flux changes, a voltage is induced in the head windings. The output voltage from the playback head is proportional to the rate of change of flux and number of wire turns the flux field lines cut through. ##EQU1## For a given degree of peak magnetization of the tape, corresponding to a particular value of alternating recording current, the peak flux in the playback head will be constant. The rate of change of flux, however, which determine the magnitude of the playback-head voltage output, will depend upon the rate of change of recording current as well as its magnitude. Therefore, if we record a varying frequency sine wave with recording current held constant regardless of frequency, the playback voltage will increase linearly with frequency. The slope of the playback voltage curve, is proportion linerly with frequency over a portion of the usable frequency range (6 db per active slope). At both very low and very high frequency the system frequency characteristic departs from this 6 db per active slope.
For low frequency response the playback heads have a maximum wave/length or minimum low frequency response, sometimes called "contour effect." The low frequency cut off is determined by three factors: 1. Length of the pole across the head face; 2. Length of the face window; and 3. Shape of lamination behind head face. All these three factors are related to the size of the head.
By moving the head out and away from the micro cassette, the present invention solves several of the foregoing, existing prior art problems. Since the head is not conventionally within the confines of the micro cassette, the head size (L) can be increased (lengthened) thereby allowing an increase in the number of wire turns (N) thereby increasing inductance (.phi.) capability and rate of change of inductance (d.phi./dt) which, of course, increases the signal (V).
In addition by moving the head distal to the tape reel motors as well as the pinch roller/capstan motor and by placing a relatively thick metal plate between the head and all electric motors and solenoids, less electrical and magnetic flux interference is encountered.
Furthermore, by wrapping the tape around the capstan, in a "U" shaped manner in the present invention as opposed to conventional tangentially touching the tape, greater tape traction is achieved with the capstan alone and therefore necessarily less capstan pressure is needed and in some cases the need for a pinch roller to apply pressure to the tape against the capstan is totally eliminated; less pressure, of course, yields less tape distortion (stretching), less tape wear and tear, less drive motor power, and correspondingly longer tape life and longer motor life.
Of equal import, is the fact that a better tape guide and tape speed control is achieved by pulling the tape out from the micro cassette past a pair of initial tape guides, across a larger head and through a large and easily positioned bidirectional tape guide.
Still another benefit achieved in the present invention is that but one tape guide is necessary to confine tape travel in two directions at a distance from the cassette, thereby eliminating excessive and needless components and further minimizing excessive tape edge wear and tear.
In addition, because the head is distal to the tape cassette/cartridge, the head can be adjusted and reoriented in three planes, zenith, azimuth and head penetration to obtain optimal signal to noise ratio thereby eliminating recording channel skew and achieving desired orientation or wrap angle of tape contact with the head.
It should also be noted that while it is common practice in the present art in tape recorders and tape playback decks to drive the tape between two tape reels past one or more magnetic heads by using a motorized capstan with a pinch roller pressing the tape against a metalic cylindrical surface of the driven capstan, so also is it common practice to utilize a frictional surface such as rubber on the cylindrical surface of the capstan to drive the tape without the use of a pinch roller by arranging an angular wrap in approach and departure of the tape from the capstan, letting tape tension and friction assist the driving force from the capstan in moving the tape.